A conventional scroll-type compressor, as shown in FIG. 4, is composed of a housing 1 which has an oil container 103 divided by an oil plate 102 mounted at the lower part of the housing 1. At the upper part of the housing 1 a stationary scroll member 4 and an orbiting scroll member 3 which have an involute or spiral shape are disposed so that the orbiting scroll member 3 orbits 180 degrees against the stationary scroll member 4. The stationary scroll member 4 is fixed to the upper part of the housing 1 which is provided with a suction pipe 100, while the orbiting scroll member 3 is engaged with a shaft 210, extending downwardly from the lower surface of the orbiting scroll member 3, driven by a motor 2 which comprises a stator 201 and a rotor 200. A slide pin 212 is provided at the upper end of the shaft 210 in an eccentric manner in respect to the center of the shaft 210. The slide pin 212 is engaged with the under surface of the orbiting scroll member 3 so that the orbiting scroll member 3 orbits around the stationary scroll member 4 by the rotation of the slide or eccentric pin 212, thereby achieving a compression of the refrigerant gas. Further, a frame 5 is employed for supporting the shaft 210, and an Oldham ring 500 is provided between the lower surface of the orbiting scroll member 3 and the upper surface of the frame 5, so that the orbiting scroll member 3 is adapted to orbit without rotating around its own axis.
According to the rotation of shaft 210 by the energization of the rotor 200, the orbiting scroll member 3 moves within the frame 5 and the refrigerant gas is drawn through the suction pipe 100. The gas is compressed at the space created by the wraps 300, 400 to be changed into a high temperature and pressure gas and is discharged to the inside of the housing 1 through an opening 402 of the stationary scroll member 4, and next the pressed gas is discharged out through the discharge pipe 101 which is mounted at the lower part of the housing 1. In addition, the oil 104 in the oil container 103 is pumped by centrifugal force in accordance with the rotation of the shaft 210. The fed up oil through the oil suction passage 211 is supplied to the place to be lubricated, thereby achieving both lubrication and cooling effects.
However, at the starting stage of the compression mode, noncompressible fluid refrigerant is fed into the pockets defined by the wrap 300 of the orbiting scroll member 3 and the wrap 400 of the stationary scroll member 4, or foreign,matter is fed into the pockets. In that case, a surplus compression is applied to the wraps 300,400 which causes an excessive force that results in the problem of a deformation and dilapidation of the wraps. Furthermore, refrigerant leakage through the gap between the wraps is increased. Accordingly, the efficiency of the compression is lowered. In the case where an invertor type compressor is used for increasing the efficiency of the compression by a variable speed motor, the centrifugal force suddenly increases when the speed of the motor slowly increases. The excess frictional force and the excess compression force occur at the wraps 300,400 to create a problem which reduces their life span.
A prior art apparatus intended to solve these problems is illustrated in FIGS. 5 and 6. An orbiting scroll member 3 comprises an eccentric slide pin 212 which is provided at the upper end of the shaft 210, a bushing 320A which is engaged with the slide pin 212 and has an elliptical hole 321, and a boss 310 which is engaged with the bushing 320A. As the shaft rotates, the orbiting scroll member 3 orbits around the center of the shaft 210. The orbiting scroll member makes a compression operation by the revolution of the slide pin. The motion relation described will now be expressed in the following equations. EQU Fc-Fgr-F.sub.R =.mu.nFn (1) EQU Fg+.mu..sub.R F.sub.R =-Fn (2)
where Fc is a centrifugal force of the orbiting scroll member
Fgr is a radial compression force of refrigerant when the refrigerant is compressed PA1 F.sub.R is a contacting force of the orbiting scroll member against the stationary scroll member PA1 .mu.nFn is a frictional force between the slide pin and the bushing PA1 Fg is a tangential force of the refrigerant in respect to the contacting force PA1 .mu..sub.R F.sub.R is a frictional force between the wraps PA1 Fn is a perpendicular contacting force between the slide pin and the bushing PA1 .mu..sub.R is a frictional factor between the slide pin and the bushing PA1 an orbiting scroll member driven by an eccentric pin formed at an upper end of the shaft; PA1 a stationary scroll member disposed in mating relationship with the orbiting scroll member; PA1 a bushing making a linear reciprocating motion by a rotating motion of the eccentric pin; and PA1 a centrifugal force control means comprising a resilient member which counteracts a centrifugal force of the orbiting scroll member and a weight balance member for counterbalancing the centrifugal force, thereby making a linear reciprocating motion independent from the linear reciprocating motion of the bushing.
The contacting force F.sub.R may be alternately expressed by using equations (1)(2) as EQU F.sub.R =(Fc-Fgr+.mu.nFg)/(1-.mu.n.mu..sub.R) (3)
where .mu.n is a frictional factor between wraps
Under the standard condition of the air conditioner i.e. .mu..sub.R =.mu.m=0.1, Fgr/Fg=0.1, the equation (3) is expressed as below EQU F.sub.R =(Fc-Fgr+0.1 Fg)/0.99 0.99 F.sub.R /Fg=Fc/Fg (4)
Generally, since the first term F.sub.R /Fg in equation (4) is larger than zero in respect to an arbitrary value relating to Fc of the second term Fc/Fg in equation (4), the sealing force F.sub.R always exists. Hence, no gap exists between the wraps, and leakage is prevented. However, as the speed of a motor increases, the contacting force F.sub.R as well as the centrifugal force Fc increase, which brings about an increased friction between the scrolls 3, 4. That is, in the case of the invertor type compressor, which varies according to the speed of a motor, the contacting force grows greater as the centrifugal force increases, which causes excess friction and abrasion between the wraps.
In order to prevent such problem, Japanese Patent Laid-Open No. 275902/1991 discloses a scroll-type compressor wherein the bushing or contraposition member is mounted on an elongated slide pin of a guide member. The guide member is mounted eccentrically on the drive shaft and is able to swing outwardly under the influence of centrifugal force to change the angular orientation of the slide pin relative to the radial direction, whereby the contact pressure of the orbiting wrap against the stationary wrap remains constant. However, at operating frequencies below the lowest frequency predetermined by the changing angular orientation, the wraps are separated from each other, and compression can not occur, which creates a loss of efficiency.